Resistive random access memories, or RRAM, are studied within the scope of non-volatile applications; they notably represent an alternative to the use of flash memories.
A resistive random access memory comprises first and second electrodes separated by a layer of active material. In the initial state, the active material is insulating (PRS, “Pristine Resistance State”). A first electrical stress is applied to the virgin resistive random access memory in order to generate for the first time a LRS (Low Resistance State). The associated process is called FORMING. The resistive random access memory may next switch from the low resistance state LRS to a high resistance state HRS by the application of a first voltage VRESET between the first and second electrodes, and switch from the high resistance state HRS to the low resistance state LRS by the application of a second voltage VSET between the first and second electrodes. It may thus be used to store binary information. The low resistance state LRS is also called “ON” state, The high resistance state HRS is also called “OFF” state.
The phenomenon of change of resistance is observed in different types of materials, which suggests different operating mechanisms. Several types of resistive random access memories may thus be distinguished. The field of the present invention more particularly relates to two categories of resistive random access memories:                memories comprising an active zone based on an active material based on oxide (OxRRAM or “Oxide RRAM”) such as a binary oxide of a transition metal;        memories comprising an active zone based on an ionic conduction material (CBRAM or “Conductive Bridging RAM”) forming a solid electrolyte with ionic conduction arranged between an electrode forming an inert cathode and an electrode comprising a portion of ionisable metal, that is to say a portion of metal that can easily form metal ions, and forming an anode.        
The change in resistive state in a resistive random access memory of OxRRAM type is generally explained by the formation of a filament of oxygen vacancies within the active zone. The change of resistive state in a resistive random access memory of CBRAM type is generally explained by the formation of a conductive filament within the active zone.
From the architectural viewpoint, a resistive random access memory is generally associated with a selection device, which may for example be a transistor or a diode. Within an array comprising a plurality of resistive random access memories, a selection device is thus provided for each resistive random access memory. Each resistive random access memory may be connected to its selection device by a connector element such as a via or interconnection hole. It then involves aligning each resistive random access memory with such a connector element. The quality of the alignment typically depends on the performances of the lithography equipment used. It is a parameter that can have an impact on the variability of the devices obtained. It is thus a potentially constraining parameter within the scope of an industrial integration. FIG. 1 shows schematically a resistive random access memory 1 comprising a first electrode E1, a second electrode E2 and a layer of active material A laid out between the first and second electrodes. The first electrode E1 of the resistive random access memory 1 is laid out in contact with a connector element C, which enables an electrical contact with a selection device, not represented,
Furthermore, numerous studies concern resistive random access memories in order to improve their reliability and their performances. One difficulty relates to the dispersion of certain electrical characteristics. An important dispersion of SET and RESET voltages and/or resistive states is in fact measured from one resistive random access memory to the next, but also cycle-to-cycle for a same resistive random access memory. One reason proposed to explain this dispersion concerns the difficulty of controlling the size and the position of the filament within the layer of active material,